The present invention is directed to a locking mechanism for use with a device for delivery of medicament, and in particular to a locking mechanism for use with a jet injector equipped with a short needle for reducing the likelihood of inadvertent contact with the needle and deter intentional reuse of die needle.
A wide variety of needleless injectors are known in the art. Examples of such injectors include those described in U.S. Pat. No. 5,599,302 issued to Lilley et al., U.S. Pat. No. 5,062,830 to Dunlap, and U.S. Pat. No. 4,790,824 to Morrow et al. In general, these and similar injectors administer medication as a fine, high velocity jet delivered under sufficient pressure to enable the jet to pass through the skin.
As the skin is a tissue composed of several layers and the injector is applied to the external surface of the outermost layer, the delivery pressure must be high enough to penetrate all layers of the skin. The layers of skin include, the epidermis, the outermost layer of skin, the dermis, and the subcutaneous region. The required delivery pressure is typically greater than approximately 4000 p.s.i. (measured as the force of the fluid stream divided by the cross-sectional area of the fluid stream).
Although this pressure is readily achievable with most injectors, there are some circumstances in which delivery of medicament to the subcutaneous region under a reduced pressure is desirable. For example, drugs that require a specific molecular structural arrangement, such as a linear protein configuration, may be rendered ineffective due to shear forces caused by the delivery of the drug at high pressures that alter the structural arrangement of the drug. As it is more difficult to deliver a large volume of fluid at a high pressure compared to a small volume, using a lower pressure facilitates delivery of a larger volume of fluid. Furthermore, the lower pressure could make manufacturing an injector device less expensive. The lower pressure would also reduce adverse stresses on the device and result in a corresponding increased useable device lifetime. Moreover, the lower pressure would make jet injection compatible with medicament stored and delivered in glass ampules, which typically cannot withstand the pressure typically reached by jet injectors.
One of the advantages associated with needleless jet injectors is the absence of a hypodermic needle. Given the aversion to needles possessed by some, the absence of a needle provides a psychological benefit. Even devices that utilize conventional hypodermic needles have attempted to capitalize on this psychological benefit. For example, self-injectors or auto-injectors like the ones disclosed in U.S. Pat. Nos. 4,553,962, 4,378,015 have retractable needles which are hidden until activation. Upon activation, the needle extends from the bottom of the device and penetrates the user""s skin to deliver medicament. As none of these devices involves delivery of the medicament using jet injection, the medicament delivery location is limited by the length of the needle. For example, if delivery in the subcutaneous region is desired, the needle must be long enough to reach the subcutaneous region. Furthermore, as auto-injectors operate like syringes, the injection time is several seconds or longer. In contrast, jet injectors typically inject in fractions of a second.
U.S. Pat. No. 5,304,128 to Haber et al. describes a jet injecting syringe that uses a short needle to assist injection. The syringe uses a gas powered driven plunger to force medication through the syringe and out of the needle. The needle is retracted until the syringe is activated and then is extended to puncture the skin of the person injected. However, the needle remains extended after the syringe is used. The extended needle could lead to potential biohazards and safety concerns, such as accidental injections and spreading of diseases. Also, the gas powered plunger is both complicated and expensive to manufacture.
PCT Publication No. WO 99/03521 of Novo Nordisk discloses an undefined concept of xe2x80x9cjetxe2x80x9d injection. However, this publication does not teach one the details of the driving mechanism necessary to practice the concept.
PCT Publication No. WO 99/22790 of Elan Corporation teaches a needle assisted injector having a retractable shield that conceals the needle both before and after use of the injector. The disclosed injector has a driving mechanism that operates on pressure created by a chemical reaction. Because of this chemically operated driving mechanism, the injecting time for the injector is at least three seconds and more likely greater than five seconds. This relatively long injection time may create discomfort in the patient receiving the injection. Also, the needle may move during the lengthy injection and add to the patients discomfort.
Even with minimally invasive medical procedures, it is advantageous to maintain the time for the procedures at a minimum. Thus, there exists a need for a needle assisted jet injector that operates at relatively low pressure and that is capable of quickly delivering medicament. There also exists a need for such an injector having a retractable or concealed needle to prevent the medical hazards associated with exposed needles. There is also a need for an injector having a retractable or concealable needle which is usable only once so that, after use, the needle is prevented from subsequent use until removed and replaced.
The present invention relates to a locking mechanism for use with a needle assisted jet injector. The needle assisted jet injector has a needle assembly with a needle and a needle guard associated with the needle assembly. The needle guard is for placement against a surface to be injected and for guarding the needle before and after an injection of the injector. The needle guard is movable between a first retracted position wherein the needle is retracted inside the needle guard, an extended position wherein the needle extends outside the needle guard for injection into the surface, and a second retracted position wherein the needle is retracted inside the needle guard after injection.
The locking mechanism includes a holder member and locking means. The holder member is configured and dimensioned to hold the needle assembly and has at least one first engaging portion. The locking member is operatively associated with the needle guard and the holder member. The locking means is preferably provided in the form of a locking member that has at least one second engaging portion for engagement with the at least one first engaging portion of the holder member in the extended and second retracted positions. The locking member is associated with the needle guard in the first retracted position, is associated with the holder member in the extended and second retracted positions, and is in blocking relation with the needle guard in the second retracted position so as to block further movement of the needle guard into the extended position and deter reuse of the needle.
The locking member may include a substantially annular portion and at least one outwardly-biased leg extending from a distal end of the annular portion. In this embodiment, the needle guard includes at least one pocket for accepting the at least one leg when the locking member is associated with the needle guard in the first retracted position. The leg maintains its position in association with the needle guard due to its outwardly-biased force and is resilient such that it is removable from the at least one needle guard pocket upon the application of sufficient force to overcome the outwardly biased force of the leg.
The second engaging portion of the locking member may include an undercut portion formed at a proximal end of the annular portion of the locking member. The undercut portion is preferably dimensioned and configured to accept the first engaging portion of the holder member for mating therewith. The proximal end of the annular portion may also include a ramp portion on an inner surface extending inwardly from the end thereof. The locking member ramp portion is angled relative to an outer circumferential surface of the annular portion for engagement with the first engaging portion of the holder member before the holder member engages the undercut portion.
The outwardly biased leg of the locking member preferably springs outwardly after disengagement with the needle guard pocket. These legs then abut a shoulder formed on an inner surface of the needle guard in the second retracted position to prevent reuse of the needle by substantially blocking proximal movement of the needle guard.
The holder member may include a substantially cylindrical portion at a proximal end thereof, the at least one first engaging portion at a distal end thereof, and an inner wall positioned substantially therebetween. The cylindrical portion and inner wall are configured and dimensioned for mating with the needle assembly.
The inner wall of the holder member may include a circular opening extending between the proximal and distal sides thereof for receiving a portion of the needle assembly therethrough. The first engaging portion of the holder member is at least one arm extending distally from the inner wall. The arm preferably includes an extension portion configured and dimensioned for seating in the second engaging portion of the locking member. The extension portion of the arm may also include a ramped portion for association with the locking member. The ramped portion of the holder member may preferably be complementary to the ramped portion of the locking member such that both ramped portions allow the other ramped portion to slide thereupon allowing the first engaging portion to engage the second engaging portion in the extended position.